1. Field of the Invention
The present invention relates to an apparatus for and a method of depositing a thin film, and more particularly to an apparatus for and a method of depositing a thin film, in which, dissimilar to a conventional technology where a gas supply and exhaust are repeated through the operation of a valve and a pump installed in a reaction chamber, a gas is continuously supplied to the inside of the reaction chamber, and the supplied gas is exposed to respective substrates through a plurality of separate reaction cells and simultaneously excessive gases are continuously exhausted, thereby improving reaction rate and characteristics.
2. Background of the Related Art
In general, semiconductor manufacturing processes employ a sputtering, chemical vapor deposition, atomic layer deposition method to thereby form a uniform thin film.
Among these thin film deposition methods, the chemical vapor deposition method has been most widely used. In this method, using a reaction gas and a decomposition gas, a thin film having a required thickness is deposited on a substrate. In the chemical vapor deposition method, first, various gases are injected into a reaction chamber, and the gases derived by a high energy such as heat, light, plasma are chemically reacted to thereby form a thin film having a desired thickness. In addition, the reaction conditions are controlled through the ratio and amount of plasma or gases applied as much as reaction energy, thus improving the deposition rate thereof. However, the reactions occur fast and thus it is very difficult to control the thermodynamic stability of atoms.
In the atomic layer deposition method, a reaction gas and a purge gas are alternately supplied to deposit an atomic layer. The formed thin film has good film characteristics and can be applied to a large-diameter substrate and an electrode thin film. In addition, this thin film has a good electrical and physical property. In general, in the atomic layer deposition method, first, a first reaction gas is supplied to chemically adsorb a single layer of first source on the surface of a substrate and excessive physically adsorbed sources are purged by flowing a purge gas. Thereafter, a second reaction gas is supplied to the single layered source to chemically react the single layer first source with the second reaction gas to deposit an intended atomic layer and excessive gas is purged by flowing a purge gas. These steps constitute one cycle of process step for forming a thin film.
As described above, the atomic layer deposition method employs a surface reaction mechanism and thus provides a stable and uniform thin film. In addition, in the atomic layer deposition method, reaction gases are separately supplied and purged in sequence, and thus particle formation can be suppressed through gaseous phase reaction, as compared with the chemical vapor deposition method.
In the case where a thin film is deposited through the above atomic layer deposition method, the deposition occurs through the materials adsorbed on the surface of a substrate (generally, chemical molecules containing the film elements). At this time, generally, the adsorption is self-limited on the substrate, and thus uniformly obtained over the entire substrate, without largely relying on the amount of supplied gas (the amount of reaction gas).
Therefore, a uniform thickness film can be obtained even in stepped portions having a very high aspect ratio, regardless of positions. Even in a case of a thin film having a thickness of a few nanometer, the thickness thereof can be easily controlled. In addition, since the thickness of the thin film is in proportion to the gas supply period in the process, the thickness thereof can be adjusted by controlling the frequency of gas supply periods.
The conventional atomic layer deposition apparatus implementing the above-described atomic layer deposition technique will be described, referring to FIGS. 1 and 2. FIG. 1 is a schematic diagram showing the structure of a conventional shower head type atomic layer thin film deposition apparatus.
FIG. 2 is a schematic diagram showing the structure of a conventional layer behavior type atomic layer thin film deposition apparatus. For the convenience of explanation, like components are denoted by like reference numerals.
First, as shown in FIG. 1, the conventional shower head type atomic layer deposition apparatus includes a reaction chamber 1 having a reaction furnace 2 where a reaction gas and purge gas is supplied in sequence and an atomic layer is deposited on a substrate 3 and connected to a pumping means for discharging supplied gas to the outside; a substrate chuck 4 provided below the reaction chamber 1 and where the substrate 3 is rested; a shower head type gas supplier 5 provided above the reaction chamber 1 facing the substrate chuck 4 and for spraying gas towards the reaction chamber 2; valves 6, 7, 8 and 9 provided on the supply path of the reaction gas supplier 5 and for opening and closing the gas supply.
Here, reference numeral 6 denotes a first reaction gas valve, 7 denotes a purge gas valve, 8 denotes a second reaction gas valve, and 9 denotes a purge gas valve.
Next, as shown in FIG. 2, the conventional layer behavior type atomic layer thin film deposition apparatus includes a reaction chamber 1 having a reaction furnace 2 where a reaction gas and a purge gas are supplied in sequence to deposit an atomic layer; a substrate chuck 4 provided below the reaction chamber 1 to allow a substrate 3 to be rested thereon; and valves 6, 7, 8 and 9 provided respectively in gas supply tubes connected so as to provide a layered form of gas to the reaction chamber 1. Here, the reaction chamber 1 is connected with a pumping means for discharging gas supplied to the reaction furnace 2 to the outside.
In the conventional apparatus having the above-described apparatuses, the reaction gas valve 6 and 8 and the purge gas valve 7 and 9 must be opened and closed every time when one cycle of operation is performed, thus shortening the service life thereof according to the service life of valves. In addition, the time for an appropriate amount of gas to reach the substrate 3 is delayed, due to the valve driving electrical signal associated with the valve operation, a time delay caused during air driving, and conductance generated in the narrow gas tubes.
In addition, since the reaction chamber 1 has a small volume for the purpose of speedy replacement of gas in the reaction chamber 1, the number of the substrate 3 capable of being mounted in the reaction chamber 1 is limited, thus leading to a decreased productivity in mass production.
On the other hand, in a conventional thin film deposition apparatus, plasma is directly excited in a reaction chamber in order to the reaction rate and the reaction characteristics in the atomic layer deposition reaction.
The above apparatus, as shown in FIG. 3, includes a plasma generator 10 for exciting plasma in a reaction furnace 2 inside a reaction chamber 1 and having a switch 11 for on and off of an RF power. In order for an atomic layer to be deposited, an RF power is to be applied, coincidentally when a selected reaction gas is introduced into the reaction chamber and exposed to the substrate 3.
In this case, problematically, the speed of the reaction gas reaching the substrate 3 is not coincident with the electrical transmission speed of the RF power. In addition, each process step is carried out in a short period of time and thus the reaction gas in the previous step is not completely removed. At this state, if a plasma is formed, a thin film comes to have a large content of impurities, thus degrading the characteristics of the thin film.
In addition, since the plasma is to be excited when the selected reaction gas is introduced, the RF power must be applied at a determined step only. Thus, in order to apply the RF power at a determined step only, on/off of the RF power must be repeated. Therefore, the RF generator for generating the RF power and the RF matching network for stabilizing plasma have a shortened service life, and the plasma formed without a stabilization time has a decreased efficiency and the atomic layer deposition reaction becomes unstable disadvantageously.
On the other hand, FIG. 4 shows a conventional thin film deposition apparatus employing a radical generator 12 capable of forming radicals on the line supplying one reaction gas. As shown in FIG. 4, in the apparatus of FIG. 4, a selected reaction gas is supplied and accumulated inside the radical generator 12 for a short period of time in order to form radicals in an external device and apply the reaction furnace, and, when a valve 13 is opened, the produced radicals are transferred to the reaction furnace 2 simultaneously.
In the case where the above-described radical generator is employed, the radicalized reaction gas is transferred to the reaction furnace through a separate valve 13, and thus the internal pressure of the reaction furnace 2 becomes unstable, in addition to the problems with durability associated with valve switching and time delay in the apparatus of FIG. 3.